1. Field of the Invention
The present invention relates to resin-molded products and methods of manufacturing the resin molded products.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2004-84503 teaches a device having a rotational angle sensor and used for detecting an open angle of a throttle valve disposed within a throttle body. The rotational angle sensor includes magnets (permanent magnets), a rotational member (a rotor) fixedly mounted to a shaft portion of the throttle valve, and a stationary member (a sensor cover) that includes a magnetic detecting element. The rotational angle of the rotational member can be used in a non-contact manner based on an output signal from the magnetic detecting element.
In some cases, the rotational member is a resin-molded product that is molded by an insertion molding process, in which resin is molded within a mold with magnets inserted into the mold. FIG. 8 shows a conventional rotational member that is a resin-molded product.
As shown in FIG. 8, a rotational member 130 has a substantially cylindrical resin body 138 and a pair of right and left magnets 134 each having a substantially quadrangular prism-like configuration. The magnets 134 are disposed on the inner circumference of the body 138 and are positioned symmetrically with each other, so that one face 134a of each magnet 134 is entirely exposed to the inner space of the resin body 138. Another face 134b of each magnet 134 intersecting with the face 134a is substantially completely positioned within the resin material of the body 138.
In the molding process to create the aforementioned structure (the resin body 130 with the magnets 134 inserted into a cavity of a mold), an unbalance can occur between the pressure of the molten resin applied to the face 134a and the pressure of the molten resin applied to the face 134b. Thus, the pressure applied to the face 134a may be low, while the pressure applied to the face 134b may be high. Due to this unbalance, a moment M may be produced to force one end (lower end as viewed in FIG. 8) of each magnet 134 in a direction radially outward with respect to the body 138 about the other end (upper end as viewed in FIG. 8) of each magnet 134. In an extreme case, the magnets 134 may be break.
Thus, there is a need in the art for resin-molded products and methods of manufacturing the resin-molded products, which can prevent or minimize breakage of magnets.